1. Field of the Invention
The invention relates to a method and apparatus for identifying words from letters entered on a DTMF pushbutton pad.
2. Description of Related Art
The concept of trying to determine the identity of a word based upon the frequency of the letters in the word is generally known in the cryptanalytical art. An interesting discussion concerning the frequency of words in the English language is found on pages 18 and 20 of the March 1988 edition of the Atlantic. For example, it is noted that nine (9) English words comprise fully a quarter of all spoken words and that forty-three (43) words account for half of the words that we use in every day speech. However, insofar as can be determined, none of the prior art appears to teach or suggest a sophisticated word guessing method and apparatus that can be employed in the context of a communications system.
The prior art also discloses some systems for using a DTMF keypad to transmit messages to a remote location where a speech synthesizer reproduces a word. Typical of such systems is the invention described in U.S. Pat. No. 4,307,266 entitled COMMUNICATION APPARATUS FOR THE HANDICAPPED. According to that invention, a sender enters the appropriate position for the letter of the alphabet to be communicated. A second entry identifies which one of the plurality of letters attached to the telephone set which decodes the two digit code entry and converts the two-digit code to a standard machine readable format which can be displayed on a standard output device such as an alphanumeric display or, for blind persons, a braille or similar output message. The sending party can transmit the message to the receiving party by keying characters into a keyboard. Keyed-in characters are converted to speech by a speech synthesizer for transmission to the receiving party. In other words, the sender types the word in DTMF code and the resultant word is reproduced at the receiving station by synthesized voice. While the foregoing system may be useful for certain applications, it seems to be rather cumbersome, limited in its vocabulary, and relatively inefficient in its transmission mode.
Other patents which discuss use of DTMF codes for transmission purposes include U.S. Pat. Nos. 4,087,638; 4,427,848 and 4,608,460.
Some attempts have been made in the prior art to identify a word from a DTMF dial tone clue. A useful description of such techniques is found in a article entitled "Digital Techniques for Computer Voice Response: Implementations and Applications", Lawrence R. Rabiner, Fellow IEEE and Ronald W. Schafer, Senior Member, IEEE PROCEEDINGS OF THE IEEE, Volume 64, No. 4, April 1976.
Of more general interest is an article entitled "Alphabetic Data Entry Via the Touch-Tone Pad: A Comment", Sidney L. Smith and Nancy C. Goodwin, The Mitre Corporation, HUMAN FACTORS, 1971, 13(2) Page 189-190.
Of general interest also are the following items from the patent literature: U.S. Pat. Nos. 3,778,553, 3,967,273; 4,012,599; 4,191,854, 4,426,555; 4,532,378; 4,557,062; 4,585,908; 4,608,457 and 4,633,041 as well as the following British Patents: 1,320,895 and 1,320,896.
Whether taken individually or as a whole, none of the prior art appears to suggest the novel apparatus and method set forth in this disclosure for efficiently identifying a word typed on a DTMF keyboard and converting that word into ASCII digital format so that it can be efficiently transported via a packet transport network to a remote location where it is converted from data to speech or otherwise delivered such as to a telex.